OrderedDict.pop() can segfault when key equality changes between lookups

Crash report

What happened?

Calling collections.OrderedDict.pop() without a default value can cause a segmentation fault if the lookup key has a stateful __eq__ implementation that returns different results across successive comparisons.

The crash occurs on the current main branch.

Minimal reproducer:

from collections import OrderedDict

class K:
    def __init__(self):
        self.calls = 0

    def __hash__(self):
        return 12345

    def __eq__(self, other):
        self.calls += 1
        return self.calls == 1

k1 = K()
k2 = K()

od = OrderedDict()
od[k1] = "value"

od.pop(k2)

Running this with a locally built CPython from main results in:

Segmentation fault (core dumped)

Expected behavior:

• OrderedDict.pop() should not crash the interpreter.
• It should either remove the matching item or raise KeyError if the key is not found.

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

Output from running 'python -VV' on the command line:

Python 3.16.0a0 (heads/fix-odict-pop-null-failobj:2ffab083782, Jul 28 2026, 12:31:11) [GCC 13.3.0]

Linked PRs

• gh-154818

从 OrderedDict.pop() 入口点开始，在本地构建的 CPython main 分支上运行最小复现程序。当复现程序不再发生 segmentation fault，并且 pop() 要么删除匹配的项目，要么在找不到键时引发 KeyError 时，即表示完成。